Info/success toasts auto-dismiss faster (3.5-4s) while warn/error
toasts persist longer (8-10s). Callers can still override with
explicit ttlMs. Dedupe, cooldown window, and MAX_TOASTS cap were
already in place from Phase 1.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds ToastProvider/ToastViewport for in-app notifications with dedupe,
auto-dismiss, and action links. Wires success toasts to issue create,
issue update, and comment mutations. Adds live event toasts for activity,
agent status, and run status changes via LiveUpdatesProvider.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>